Recovery of sodium sulfate and hydrochloric acid from acidic sulfate waste materials



United States Patent RECOVERY OF SODIUM' SULFATE" HYDRO- CHLORIC ACIDF'ROM ACIDIC SULFATE WASTE MATERIALS;

John C. Bcrnert,.Niagara: Falls, N. Y., assignor to-Hnoker Electrochemical Company, Niagara" Falls, N Y., a corporation of New'York No Drawing. Application November 17, 1954, Serial No. 469,534

This; invention. relates: to the: disposal. of acidic; sulfate waste materials and ismore particularly concerned with suclr process: which utilizes. commonly available: sodium salts and which prepares chemicals having economic value.

Many. commercialprocedures today prepare as, a wastelay-product; an acidic: sulfate material such as a mixture: ofv sodium, hisulf'ate containing. sulfuric acid, or sulfuric:

acid contaminated witliby-products making, it unsuitable:

for re-usevi'n the: origjiualtprocess; For example, in: the: production of chlorine. dioxide from sodium. chlorate, most: processes use asulituricracid reaction medium,,whichi is separated from the reacti'on'mixtune containing large: quantities of; sodium. bisulfate: and other; contaminants; The disposal. of this. materialv presents. a serious prohl'enu, because of high acidity. Where chlorine dioxide, is generated for. paper pulp. mills, these same; pulp: mills use large; quantities. of sodium sulfate. Even: though both: sodium and sulfate ions are present in the acidic sodiiuns bisulfate waste, no economical processhas heretofore been provided for the conversion of the waste acidic sodium bisulfate to prepare sodium'sulfate.

It is a principalohject of the present invention to provide aprocess for the conversion of acidic sulfate materials including-sulfuric acid and sodium hisulfate, into useful" products having economic value. Another object of the present invention is to cause such conversion using readily available materials. Still a further object of. the present invention is to provide such a process which involves refrigeration of aqueous solutions'and. separationoffa crystallizate. Another object of the present inventionis to provide a process. for the preparation of aqueous: solutions of. acids. Other objects will become apparent hereinafter.

The foregoing and. additional objects have been acconr plished by providing an aqueous solution of an acidic sulfateanda sodium salttof" an acid; coolingj'this solution to atemperature such'that crystallization of sodium sulfate. occurs, and separating the crystall'izat'e.

sulfuric. acid, sodium .bisulfate trisodium hydrogen disulfate, .or miittures offany, of'these materials- The presence ofiotlier materials in an amount less thanwill cause" undesirable.amountsroffcontaminants at the temperature :that the. crystallizatee is. separated from the liquor are also included. Sodiunxsalts. of acids, which; are suitable are thosetwhichlare solubleinwater and which form a Watersoluble acid such 1 as,;. for. example'sodium. chloride,

sodium bromide, sodiumt iodide, sodium nitrate, t. sodium 1 jfuric acid ct ceterag; to prepare starting solutions ha 'ng' ice 2'. fol-mate, sodium acetate, sodiunrpropionate, sodium bro mate, sodium: iodate; et ce'tera, preferably, sodium clilo rider as'r being" the cheapest and most readily available; 'Qfi course. thBi particular salt: which is employed will: form the: acid oh the anion and: the: selection ofi a salt may be governed by the acid: desired,

These materials are mixed,- in an. aqueous, solution desirablyin an amount such that the ratioof sodiumion mole concentration is equal to two times the sulfate ion mole concentration. That is, all of the sodium and sulfate ions present can form sodium sulfate ('NagSOg); It is to be understood that other ratios such as 3.0 to 1.0 or- 1.5: to 1.0 are operative, however, at the higher ratio of sodium ion, the crystallizate= a t-l'ower temperatures may be contaminated with. the sodium salt of the" aci introduced into solution, while if an excess of sodium. ion is introduced at: the lower temperatures, less sodium: sulfate can be. crystallized causing unduly great contamination of the acid} solution. Further. in is desirablethat thesu-lffate, ion concentration be; rather concentrated else on cooling an excessive amount ofiice is, formed, prior to the, formation of? sodium sulfate. The sulfateioti mole concentration: can vary from one h'alfj mol'e er liter to over 2 :25 moles per liter and preferably there is at? least 1125. mol'esa per liter present. Oneamanner of maintaining the sodium and sulfate ionsin proper ratio is-toapproximate the amount'required, incrementally cool the solution partway; remove the? crystals, and, adjust the concentration} ofl sodium. or sulfate. ion in the mother liquor. Then, of course, cooling the adjusted liquor? result in a material which can be cooled very low without-crystallizationof undesired products.

While the temperature employed will'b'e that temperature at which an aqueous solution. of acid having the desired purity is provided, for purposes of illustration, it is herein assumed that the starting solution is at room temperature and that this solution is cooled to a pointto separate as much as conveniently possible-of the sodium and sulfate ions; Because of the large amount; of crystalli-za-te which forms-it?" is oftentimesmore practical" to S remove the crystals incrementally. Thus; if desired; a starting solution may be cooled to a minus twenty-(-20) degreescenti'g rade and the crystals removed; Then, the mother: liquor cooled further and thenewly-forh'r'ed crysta ls: are removed; Alternatively; where a relativelyconcentralized-solution is provided, cooling to aboutzero ((l) degrees centigradewill'producea largequantity' of crystals to'heremovedi The sodium sulfate will crystallize as the hept'aliydi'ate, dehydrate, or mixtures-- of these two material'si com/er sion of the hydrates toa'nh-ydrou's sodium-- sulfate-may he accomplished-- in conventional manner. The solution which remains after separation of the crystals will he an acid solution having an anion corresponding to the sodium: saltintroduced. 1 This acid solution, as: well: as the sodium :sulfate, has utility in the usual applicati ons ofsuch materials.

In the following examples, which are given by way of illustration only,, and which are" not to heconstruech as limiting,-all chloride is calculatedas hydrogemchloride, and all! sulfate is: calculated as sodium" sulfate, unless an excess of sodium is? present, which is calculateda's sodium chloride,- Whilean excess of sulfate=- is. calculatedas; sulf'uric acid;

EXAMPLE. 1

Several solutions of sodium chloridewere-treatedwith various acidic sulfates, including sodium hisulfate; sulvaryingt compositions. Where" necessary; the soiiitio'iis were heated to cause solution of all the ingredients and clarified by filtration. In each instance the-solution had COMPOSITION OF CRYSTALS (IN GRAMS) a volume of one liter at twenty (20) degrees centigrade. R S T These solutions were then cooled to about minus twentytwo (22) degrees centigrade and where super cooling 17 2 15 1 31 occurred, crystallization induced by seeding, or by agita- 5 216 15210 18711 tion. When equilibrium between the solid phase and 3 3 liquid phase had been achieved, which usually meant maintaining the low temperature for several hours, the COMPOSITION OF CRYSTALS mixture was filtered, taking care to prevent warming and B90 10 H2O the mother l1quor analyzed. The crystals were washed 1.2 0.9

and then analyzed. For convenience, the results of 2%;

several runs performed may be tabulated as follows:

Table I ABODEFGHIJKLMNOPQ Compositions of Starting Solution (grams/liter):

Hot 106.4 101.4 102.0 99.9 96.0 39.3 34.1 122.3 119.3 115.3 111.1 105.5 103.5 101.4 32.2 100.3 106.5 H1804. 1.5 0 10.3 2.5 2.4 2.3 2.2 0 0 0 0 0 0 0 0.6 0 0 NaCl 0 16.4 0 0 0 0 0 3.2 3.2 3.0 2.9 2.7 2.7 2.6 0 2.64' 2.3 NmS0 207.3 197.5 193.7 194.6 137.0 175.0 163.3 233.2 233.4 225.6 216.4 205.5 201.6 197.5 320.2 196.3 207.5 40 374.0 374.7 379.0 331.0 334.6 391.9 900.0 356.3 359.6 363.6 369.6 376.3 379.2 332.5 359.0 334.3 377.2 Specific Gravity 1.190 1.190 1.190 1.173 1.170 1.159 1.150 1.220 1.216 1.203 1.200 1.190 1.137 1.134 1.262 1.134 1.194 Compositions of the Filtered Liquors (gram /liter):

HCl 140.7 135.6 133.4 127.6 120.3 113.1 116.6 159.6 160.4 157.2 144.3 133.9 136.3 131.9 144.3 133.9 142.9 2.0 1 0 15.7 3.1 1.3 3.3 2.3 10.9 0 0 0 0 0 0 3.0 0 0 0 19.9 0 0 0 0 0 0 2.9 2.9 2.4 3.5 3.5 2.9 0 1.6 1.2 63.6 47.3 53.3 47.6 53.6 59.3 64.0 39.0 106.3 34.4 39.7 72.3 66.5 63.2 30.2 59.5 67.7 903.7 906.7 902.1 931.7 927.3 919.3 919.6 330.5 377.4 337.5 895.6 903.2 903.2 910.0 394.5 903.0 900.2 1.110 1.110 1.110 1.110 1.103 1.100 1.103 1.140 1.147 1.132 1.132 1.113 1.110 1.103 1.222 1.103 1.112 .756 .743 .764 .733 .793 .761 .721 .729 .747 .736 .770 .759 .756 .769 .570 .753 .745

Composition otC stals Na-1SO4(XH2OX= 10.0 10.0 9.65 9.97 10.0 9.09 10.0 10.0 10.0 N301 (percent) 0.28 0.2 0.3 0.5 Ice(percent) 2.5 1.0 1.2 0.02 2.5 2.0 Yield (percent) 66.0 72.3 63.1 73.3 75.1 75.4 35.7 77.2 75.66

' EXAMPLE 2 Several of the filtered liquors of the above Example were combined to yield two portions containing one liter each of solution having the composition shown at R and T in the following Table 11. One portion was cooled by stirring with a test tube filled with solid carbon dioxide to minus thirty-one (31) degrees centigrade, the crystallizate separated by filtration taking care to avoid warm- .ing of the mixture, and the mother liquor analyzed. Thereafter, this mother liquor, having the composition shown at R was cooled to minus forty (-40) degrees centigrade and the crystallizate separated again, taking care to prevent warming of the mixture. The results of this second separation are shown at S. The second por' tion of combined filtered liquors was cooled directly to minus forty (40) degrees centigrade by stirring with a test tube containing solid carbon dioxide and the crystallizate separated as above. The results of this separation are shown in the following table at T.

Table II COMPOSITION OF STARTING SOLUTION (GRAMS/LITER) In the manner of the foregoing Examples, other sodium salts, such as sodium iodate, sodium bromate, sodium nitrate, et cetera, will produce aqueous solutions of the corresponding acids and sodium sulfate.

vVarious modifications may be made in the method of the present invention without departing from the spirit or scope thereof and it is to be understood that I limit myself only as defined in the appended claims.

I claim:

1. A process for the conversion of wastes containing primarily acidic sulfates which comprises: providing an aqueous solution containing sulfate, chloride, hydrogen and sodium ions, the ratio of sodium to sulfate ions being between 3.0 and 1.5 to 1.0, and the sulfate ion is present in an amount of from 0.5 to about 2.25 moles per liter, cooling the solution to below minus fifteen degrees centigrade, and separating the crystals which form thereby to provide an aqueous solution of hydrochloric acid.

2. The process for the conversion of wastes containing primarily acidic sulfates which comprises: providing an aqueous solution containing sulfate, chloride, hydrogen and sodium ions, the ratio of sodium ions to sulfate ions R s T being approximately 2 to l, and the sulfate being present in an amount of from about 1.25 to about 2.25 moles 135. 2 142.1 135.2 per liter of solution, cooling this solution to a temperature 8 g 3, below minus twenty (20) degrees centigrade, and, sepa- 61.4 46.5 61.4 rating the sodium sulfate crystals thus-formed thereby to 9 5 893 9 provide an aqueous solution of hydrochloric acid. I 3. A process for the conversion of wastes containing COMPOSITION OF FILTERED LIQUORS (GRAMS/LITER) primarily acidic sulfates which comprises: providing an Tempmwmnegmesc aq s hgt cqntalnmg a chlorlde, y o n HG] 142.1 165.0 166.2 and sodium ions, the ratio of sodium ions to sulfate 1on3 0 being approximately 2 to l, and the sulfate being present NaCl 0 0 .0 M14304--- 46.5 37.0 37:1 1n an amount of from about 1.25 to about 2.25 moles per gig- 333 8 fibg liter of solution, cooling this solution to a temperature of Volume (liters) .951 .855 806, approximately minus twenty (20) degrees centlgrade, 1 "5 separating the crystals which form, adjusting the sodium and sulfate ion concentration to about 2.0 to 1.0, cooling the liquid remaining to minus forty (40) degrees centigrade, and separating the crystals thus-formed thereby to provide an aqueous solution of hydrochloric acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,863,172 Stockly et a1 June 14, 1932 1,958,760 Martin May 15, 1934 1,971,754 Martin Aug. 28, 1934 2,275,825 Lewis Mar. 10, 1942 Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans, Green and Co., New York, 1922, vol. 2, pages 667, 678-682, 657.

Smith: Inorganic Chemistry, Appleton Century Co.,

10 New York, 1937, pages 206, 207, 208.

U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,816,829 7 December 1'7, 195'? John C. Pernert It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let ters Patent should read as corrected below.

Column 2, line 50, for "dehydrate" read .--decahydrate--;

Signed and sealed this 25th day of February 1958.

(SEAL) Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents 

1. A PROCESS FOR THE CONVERSION OF WATER CONTAINING PRIMARILY ACIDIC SULFATES WHICH COMPRISES: PROVIDING AN AQUEOUS SOLUTION CONTAINING SULFATE, CHLORIDE, HYDROGEN AND SODIUM IONS, THE RATIO OF SODIUM TO SULFATE IONS BEING BETWEEN 3.0 AND 1.5 TO 1.0 AND THE SULFATE IONS BEING IN AN AMOUNT OF FROM 0.5 TO ABOUT2.25 MOLES PER LINTER COOLING THE SOLUTION TO BELOW MINUSFIFTEEN DEGREE CENTIGRADE, AND SEPARATING THE CRYSTAL WHICH FROM THEREBY TO PROVIDE AN AQUEOUS SOLUTION OF HYDROCHLORIC ACID. 